In recent years, printers using sprayable inks, such as the ink jet printer, have come into general use. These printers, which employ ink jet heads having small orifices that propel inks in a continuous stream of drops or in minute individual drops on demand, are used in various electronic printing applications. They offer not only high speed but quiet operation without the need for external developing or fixation procedures. Thus, ink jet printing is highly suitable for electronic printing in applications such as computer aided drafting, architectural renditions and seismographic recording.
Although transparent films are available for ink jet applications, they lack the necessary qualities for engineering and its allied applications. In order to realize the full potential of these applications, ink jet films must provide imagery of sufficient density and resolution and a surface suitable for ink and pencil annotation. Ink jet prints may be used as "originals" much like those of hand rendered drawings. In addition, they must be able to serve as "intermediates" suitable for transmissive and/or reflective copying. This latter requirement relates to engineering applications where it is a common practice to use an intermediate as the master to produce many release copies. These copies are then distributed both internally and to manufacturing subcontractors, among others. Changes and additions may be made on the intermediate prior to its use as a master for making copies.
Ink jet systems employed in informational electronic printing are comprised of three components: the printer, the ink and the receptor sheet. The printer controls the size, number and placement of the ink droplets and contains the transport system. The ink provides the colorants which form the image, and the receptor sheet provides the medium which accepts and holds the ink. The quality and archivability of ink jet prints is a function of the total system. However, the composition and interaction of the ink and the receptor material most affect the quality of the imaged product.
Ink compositions which are useful in ink jet recording systems are well known and generally contain water, organic solvents and dyes. There is thus disclosed, for example, in European Patent 0,294,155, an ink jet composition useful in ink jet recording consisting of water based vehicle containing about 30-99% wt. water with the balance made up of high boiling solvents such as glycols, glycol ethers, pyrrolidones and surface active agents. For engineering and allied uses, the inks employed contain preferably acid or direct dyes and are most generally black, though colored inks are sometimes utilized. So called "solid inks" are beginning to be employed and are contemplated in this invention.
Film recording media represent a special problem in ink jet recording because their surfaces are hydrophobic or quasi-hydrophobic. Even when surfaces are treated with special coatings to accept and absorb the inks, it is difficult to obtain the requisite qualities of image density and resolution without incurring offset, smear, bleed or other undesirable properties.
Ink jet printers apply small ink droplets in a selective pattern to form the images. These droplets are absorbed into the coating on the film surface. After initial absorption, the dye continues to spread laterally. Concurrent rapid diffusion into the film matrix is also important to avoid smear and offset. Thus, the ink absorptive qualities of the ink receptive matrix of the film is of paramount importance.
There is considerable literature which describes attempts to provide the optimal receptor sheet. A general approach to the problem of hydrophobic surfaces is discussed in U.S. Pat. No. 4,503,111, which teaches the use of a surface coating to absorb the ink. In addition, a wide variety of polymers alone or in admixture have been proposed for use as surface coatings; see for example, U.S. Pat. Nos. 3,889,270; 4,555,437; 4,564,560; 4,649,064; and 4,578,285. Multiple coatings have also been employed in trying to overcome the various problems associated with hydrophobic nature of recording media; illustrative of these coatings are U.S. Pat. No. 4,379,804, Japanese Patent No. 01041589 and Japanese Disclosure Numbers 86-86-074879 and 86-41549. Coatings containing inorganic fillers are disclosed in U.S. Pat. Nos. 4,481,244, 5,002,825 and 5,013,609.